The development of new color switching system that reversibly change color in response to external stimuli, such as electric or magnetic field, mechanical stress, temperature change, or chemical reaction, has attracted a great deal of attentions for their important applications in sensing devices, display and signage technologies, rewritable media, and security features.
For example, a particularly intriguing possibility is offered by light-responsive materials, which can be remotely controlled and rapidly changed in a clean and non-invasive manner without the need of direct contact with the system. Many organic compounds that show photoreversible color switching properties, such as some anilines, disulfoxides, hydrazones, osazones, semicarbazones, stilbene derivatives, succinic anhydride, camphor derivatives, o-nitrobenzyl derivatives and spiro compounds. Some of the most common color switching processes involved in the these organic compounds are pericyclic reactions, cis-trans isomerizations, intramolecular hydrogen transfer, intramolecular group transfers, dissociation processes and electron transfers (oxidation-reduction).
Efforts have been devoted to improving the properties of the color switching organic compounds to fulfill the requirements of the different applications. However, the practical application of these organic compounds in sensing devices, display and signage technologies, rewritable media, and security features can have challenges, for example, (i) most of these organic molecules depends strongly on the environment properties in which they are dissolved or allocated, such as the polarity, pH value, solubility, temperature and etc., (ii) organic compounds experience competing thermal back relaxation and sometimes other side reactions which, although slow, are unavoidable and give rise to serious problems such as lack of stability and controllability, leading to low efficiency both in color switching rate and cycling performance, (iii) color switching often becomes much slower when organic compounds are present in solid media instead of solution since their molecular mobility is dramatically restricted, and (iv) high cost associated with the complex synthesis of organic compounds.